Method and apparatus for making dynodes



' Dec. 12, 1950 w. S. MLEAN METHOD AND APPARATUS FOR MAKING DYNODESFiled Nov. 16, 1948 W/ZL/AM f. MC LEA-N INVENTOR.

/4 T TOP/V5 Y Patented Dec. 12, 1950 METHOD AND APPARA'EUS FOR MAKINGDYNODES William S. McLean, Woodbury, N. J., assignor to National UnionRadio Corporation, Orange, N. 3., a corporation of Delaware ApplicationNovember 16, 1948, Serial No. 60,333

5 Claims.

This invention relates to electron emitters, and more particularly itrelates to methods of preparing emitters of the secondaryelectronemissive. type such as dynodes and the like.

A principal object of the invention is to provide a simplified method.of producing secondary electron emitters or dynodes.

Another object is to provide a method of producing dynodes whereby theycan be manufactured in large quantities with a high degree of uniformityin their secondary electron-emissive powers during their useful life. IA feature of the invention relates to a secondary electron emitter ordynode, comprising a base of oxygen free' copper having a thin layercomprised of barium and magnesium oxides.

Another feature relates to a method of preparing dynodes so as toproduce a secondary emission ratio ranging uniformly between certainvalues, for example 4 to 6, and wherein the completed dynode is capable,of withstanding high heat dissipations without affecting the secondaryemission uniformity during its useful life.

A still further feature relates to the novel organization, andsuccession of apparatus and method steps which cooperate to provide animproved secondary electron emitter or dynode.

Other features and advantages not particularly enumerated, will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing,

Fig. 1 is an elevational view, partly in section, of a preferredorganization of apparatus used in practicing the invention.

Fig. 2 is a sectional View of Fig. 1, taken along the line 22 thereofand viewed in the direction of the arrows.

The dynode prepared according to this invention may be of any desiredshape and size, and consists of a base or backing of oxygen-free copperhaving a coating of barium and magnesium oxides deposited thereon, alsoin accordance with the invention. Thus, a copper member in the form of astrip or sheet of the desired shape and size, is first polished on theside or sides intended to receive the secondary-emissive ma terials. Anywell-known mechanical polishing process may be used if the surface isinitially rough, and any well-known polishing material such as that soldunder the trade-name Tripoli may be used, in conjunction with a hardbufiing wheel. When the initial roughness has thus been removed, thesurface is finished 2 with jewelers rouge in conjunction with a softcotton polishing wheel. If the initial surface not too rough, it may benecessary only to polish it with the jewelers rouge and the soft bufiingwheel.

The polished copper base or backing is then degreased by means oftrichlorethylene or similar degreasing agent, care being taken thatduring this stage of the process, contamination of the polished surfaceis avoided. The polished and degreased member is then fired in areducing atmosphere, for example, in a hydrogen furnace of anywell-known construction, at a temperature of approximately 600 C. forapproximately one-half hour.

' The next step is to mount the member within a bulb which can besubjected to evacuation. For example, as shown in Figs. 1 and 2, thememeber which has been polished and degreased and subjected to thehydrogen firing, is attached by any well-known means to a Wire or othersupport 2 which is anchored or sealed in the press 3 of any well-knownform of a glass bulb 4 of any suitable shape. The press 3 in theconventional way, is sealed to the glass bulb 4 and is provided with theusual exhaust tubulation 5 by means of which the interior of the bulbcan be evacuated. Also mounted on the press 3 is a bafile plate 6 whichmay be manufactured of carbonized nickel, and having slightly-bent edgeportions 1, 8, which act as directors of the flashed material so as toconfine it substantially to the surface of dynode I facing the baffie.Attached centrally to the bafile 6 is a wire loop 9 which is formed of abarium-bearing material which when vaporized or flashed, releases bariumvapor in the well-known manner. Preferably, the loop 9 is formed of Type66I3 barium getter, manufactured by Kemet Laboratories, Ltd, Cleveland,Ohio, and identified under the trade-name Kemet Kic Getter. If desired,the U-shaped portion of the loop may be made out of carbonized nickelwire, and the barium wire may be in the form of a straight length i0which is suitably welded to the lateral arms of the U-shaped frame. Inany event, the barium-bearing getter is formed as part of a completeinductive loop which can be raised to a flashing temperature by asuitable high frequency induction coil, the amount of heat generated inthe getter loop being determined by the orientation of the highfrequency magnetic field with respect to the loop. Also attached to thebafile 6 is a metal flag H inclined towards the dynode, asshown inFig. 1. Suitably attached .mately one-half hour.

3 to the forward end of the flag H is a quantity of another material l2which is of a type which releases magnesium vapor when flashed. Thematerial i2 can be flashed independently of the material it by properorientation and location.

of suitable high frequency induction heating field produced for exampleby the bombarding coil 63 which can be brought into relatively closeproximity with the member H to heat the material I2 to flashingtemperature without affecting the loop 9. When it is desired to flashthe material in loop 9, another coil M can be positioned so as tocontrol the amount of heat generated in the said loop to control thedegree of flashing of the getter material therefrom. It will beunderstood, of course, that the man ner of selectively and independentlyflashing the two materials is merely illustrative, and any otherwell-known manner of timing and independently flashing the materials maybe employed. After the various parts have been mounted within the bulb 4as abovedescribed, the bulb is evacuated and baked-out at a tem peratureof approximately 300 C. for approxi- The coil It, such as isconventionally used in radio tube manufacture, issupplied with highfrequency heating current, so as to' heat the member I by high frequencyinductive heating to a relatively high temperature, for example 850 C.to 875 C. at which it is-"outgassed. As a result of this heating, themember I is thoroughly degassed, and this bombarding process may berepeated several times until the degassing is found to be complete. The

heat developed during this .outgassing is con trolled so that it doesnot flash either of the materials to be subsequently flashed.Thereafter, the members 9 and i i are also subjected to high frequencyheating but to a temperature merely sufficient to degas them withoutactually raising-th'em to a temperature suflicient to flash either ofthem.

When all the parts within the bulb 4 have been thus degassed orbombarded, the bulb and its contents are allowed to'cool forapproximately ten minutes. Thereafter, the loop 9 is lightly flashed,that is to say, it is subjected to heating for a relatively short periodof time just sulficient to vaporize a relatively small portion of thebarium therefrom. After the light or partial flashing of the materialfrom loop 9, the getter material i2 is heavily flashed, that is to say,it is heated. rapidly to a very high temperature at which substantiallyall of the magnesium therein is vaporized and flashed. During theabove-described flashing operations, the member t is unheated andtherefore the flashed barium and magnesium metals condense or deposit onthe member i. By reason of the relatively concave arrangement of themember I and the concave arrangement of the baffle 5, the flashedmaterial is substantially confined to the surface of member I facing theba-file, and very little getter material is deposited on the oppositesurface of the said member After the heavy flashing of the material It,the material in loop is again flashed, this time heavily, or to a high"temperature, so that substantially all the barium is vaporized anddeposited on to the member I. After the flashing and deposition of themagnesium and barium on the member I, the parts are allowed to cool. Ineffect, therefore, the dynode is coated with a thin secondaryelectronemissive layer comprising a thin under-stratum bombardingoperations.

of barium, an intermediate-stratum containing magnesium, and anover-stratum of barium.

The member i which is not yet oxidized is kept within an evacuated bulb1 until ready to be used in its final device. If desired, the tubulation5 can be sealed-off after the flashing is complete. When the dynodemember thus prepared is ready for assembly into its final device or tubestructure, the bulb 4 is broken, and the dynode l is removed therefromtaking care that its surface be not contaminated by handling. It is thenassembled in its proper position in the final device or tube. In anyevent, it is found that the best results are obtained when theabove-mentioned step of firing the backing member I, and the flashingoperations above described, are not too far apart in time, preferablywithin twenty-four hours of each other, and the dynode which is not yetoxidized should be kept in the sealed evacuated bulb until ready foruse. After the prepared dynode has been removed from bulb 4, it shouldnot be exposed to air longer than six hours. However during thisexposure, the outer barium and some o'f'the magnesium are oxidized toproduce the desired barium and magnesium oxides. While the manner inwhich the magnesium is oxidized, at least in part, is not fullyunderstood, it is believed that during the deposition of the flashedbarium thereon, some of the magnesium diffuses into the surface portionof the barium.

When the dynode has been assembled in a finished secondary emissiontube,,care should be taken'not to overheat the surface of thedyn'odowhen the secondary emission tube is being subiected to the conventionalheat treatment or Preferably, the finished electron tube with its dynodeis subjected tothc usual aging operation, and it has been found thatduring this operation the surface of dynode must not be overloaded to anextent exceeding .1 watt per square centimeter during the first tenhours of operation.

It has been found that dynodes prepared according to the foregoingprocess are capable of producing values of secondary emission ratioranging uniformly from 4 to 6, and the finished dynode surface has beenfound to withstand heat dissipations of .5 watt per square centimeterfor periods of 500 hours or better without sub stantial change of theuniformity of its secondary emission powers.

While certain specific embodiments have been described herein, it willbe understood that various changes and modifications may be made thereinwithout departing from the spirit and scope of the invention.

What is claimed is:

1. A secondary emission dynode-forming member consisting of a backingmember of oxygenfree copper having a thin coating of secondaryelectron-emission material said coating comprising an underlayer ofbarium, an intermediate layer containing magnesium, and an overlayer ofbarium.

2..A. dynode-forming member according to claim 1, in which the saidunderlayer of barium is substantially thinner than the said outer layerof barium.

.3. The method of coating a dynode with sec ondary electron-emissivematerial which come prises mounting the dynode in an evacuatedreceptacle in spaced relation to a barium-bearing material and aseparate magnesium-bearing material, first flashing the barium-bearingmavaporizable materials whose oxides are efilcient secondary emitters,partially flashing one of the materials, fully flashing the othermaterial, and

then fully flashing the first material.

5. The method of manufacturing a secondary emission dynode, whichcomprises mounting a metal support backing in an evacuated receptacle inspaced relation to a barium-bearing material and to a separatemagnesium-bearing material, first flashing the barium-bearing materiallightly to deposit a relatively thin coat on" the surface of saidbacking, then flashing the magnesium-bearing material heavily to deposita relatively thick coat of magnesium over the said thin barium coat,then flashing the bariumbearing material heavily to deposit over themagnesium coat a coat of barium which is much thicker than thefirst-mentioned barium coat, and then subjecting the coated dynode to anoxidizing atmosphere to convert the exposed barium coat and at leastpart of the magnesium coat to their respective oxides.

' WILLIAM S. McLEAN.

REFERENCES CITED The following references are of record in the .file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,178,232 Hickok Oct. 31, 19392,178,233 Klatzow Oct. 31, 1939 2,293,177 Skellett Aug. 18, 19422,297,467 Gorlich Sept. 29, 1942 2,422,427 Louden June 17, 194'!

